a) Field of the Invention
The present invention relates to a character string recognition method and a character string recognition device for optically reading a character string on a medium such as paper or plastic. Specifically, the present invention relates to a character string recognition method and device that are capable of preventing from reducing recognition accuracy.
b) Background of the Related Art
Character string recognition devices for recognizing a character string which is printed on a surface of a medium such as a check have been conventionally known. For example, a character recognition device which is disclosed in Japanese Patent Laid-Open No. Hei 05-120483 includes a character cutout means which detects a character portion from binarized image data and cuts out the character portion along a circumscribing rectangular frame, a feature vector extraction means which extracts a feature vector from a character pattern obtained by the character cutout means, a feature storage means which has stored features for every character in advance, a similarity computing means which obtains a similarity of the feature vector of the inputted pattern with reference vectors for every character in a feature dictionary, a candidate character selecting means which selects a candidate character on the basis of a degree of similarity obtained by the similarity computing means, and a similar character recognition means which recognizes in detail when a plurality of candidate characters are selected by the candidate character selecting means. According to the character recognition device having the structure as described above, a character string printed on a surface of a medium can be recognized.
The binarized image data described above are obtained by an optical sensor for optically reading a character string printed on a medium. Specifically, from a viewpoint of reducing a manufacturing cost, it has been known to often use a CCD line sensor (one-dimensional imaging element) for optically reading a character string one-dimensionally (see, for example, Japanese Patent Laid-Open No. Hei 05-73722). In this case, a main scanning on the character string on the medium is performed by the CCD line sensor and a sub-scanning is performed by medium movement based on a manual operation or a mechanical drive operation. In this manner, two-dimensional image data of the character string are obtained by mutual operations of the CCD line sensor and the medium movement and then the two-dimensional image data are binarized and the binarized image data described above are obtained.
However, there is a problem that a high degree of recognition accuracy is not attained in the latter conventional character recognition device described above.
Specifically, in a manual type card reader, when a medium carrying speed varies due to a manual operation (swipe operation in a swipe type card reader) to cause distortion of image to occur in a medium carrying direction, distortion of image may simultaneously occur in a direction perpendicular to the medium moving direction (for example, image may be inclined or waved). Further, distortion of image may occur in the direction perpendicular to the medium moving direction even when an under face of the medium is floated from a carrying passage face in an imaging device (character recognition device). In this case, since a direction of the image distortion is a direction perpendicular to the medium moving direction, it is difficult to correct the distortion. For example, in the latter conventional character recognition device, an image distortion in the medium moving direction can be corrected but, when the image distortion is a direction perpendicular to the medium moving direction, correction is difficult. As a result, when cutting-out for characters is performed by using the distorted image, recognition accuracy may be reduced.